1. Field of the Invention
The invention relates to a reinforcement element made of a composite material particularly adapted to an application to a boot or binding using tightening straps. In addition, the invention relates to a method of manufacturing such reinforcement element.
2. Description of Background and Relevant Information
Currently, reinforcements used in boots, for example, in the area of the heel or as a tightening flap, are manufactured by injection molding a polymeric material, such as polyurethane (PU), polyether amide or a thermoplastic polyester (for example, a material commercially known as HYTREL).
Such reinforcements have the drawback of being very expensive to make, particularly due to the investment needed for injection molds.
It is also known in the field of walking/hiking boots to have outer tightening flaps made of synthetic material. Such tightening flaps are disclosed, for example, in French Patent Publication Nos. 2 694 167 and 2 749 739.
These tightening flaps are fixed, at a lower end, either on the upper or between the upper and the outer sole, as a lasting allowance, and have, at their upper end, keepers or the like that are capable of cooperating with tightening means of the lace type. These tightening flaps fulfill both functions of tightening and protecting the foot.
In the example of FR 2 694 167, the tightening flap is arranged asymmetrically and is made of polyurethane. However, due to the elasticity of this material, the tightening effect obtained was too substantial, as the PU flap stretched during tightening and then retracted, thus causing a tightening tension that was too substantial.
In the example described in FR 2 749 739, two-thirds of the height of the tightening flap are fixed to a thin plate of the same material, and its elastic length is therefore greatly reduced.
Such tightening flaps could also be made of polyether amide (such as the material commercially known as PEBAX) which are less elastic, but very expensive materials.
Therefore, polyurethane is generally the preferred material because of its mechanical properties and resistance to wear. Nevertheless, it is still expensive to implement since it requires injection molds.
In addition, its relative elasticity requires making reinforcements having a substantial thickness or complicated shapes if one wishes to have a sufficient resistance to traction.
It is also known from various patent documents, particularly European Patent Publication No. 697 957, to make boots by injecting polyurethane on a sock-shaped inside of a mold. Such three-dimensional injection methods require very complicated and expensive molds. Additionally, the sock on which the polyurethane material is injected is necessarily made of an extensible material, particularly to allow demolding the boot and the flexion thereof in certain zones.
As for the tightening straps for bindings, particularly those for snowboard bindings, they must meet very contradictory requirements. Indeed, they must first of all ensure a hold in traction of the boot on the sporting article and must therefore be inextensible. Furthermore, they must ensure anchoring of the linking/tightening members, such as binding screws, a ratchet tightening system, etc, to the sport article without material creeping. They must distribute the tightening pressure over the foot so as not to create a painful pressure spot. They must be supple in torsion and in flexion, having no hard spots, particularly in the area of the zone for fastening the linking/tightening members. These different requirements are generally met by a stacking of different layers, each one of which ensures one of the desired functions.
Thus, the strap generally has:                a foam, normally lined, for comfort and for avoiding pressures that are too localized;        inserts arranged in the area of the zones for anchoring the linking/tightening members of the strap;        an inextensible reinforcement arranged either on the inside of the strap between two foam layers or on the outside.        
Such a construction is very expensive due to the stacking of layers and the number of connections by stitching that are necessary between these different layers.
Furthermore, it does not allow much flexibility as to the shape of the reinforcement. Commonly owned with the present application is French Patent Patent No. 2 831 068, which proposes improving the insert by adding to it at least one transverse tongue so as to confer to it a rigidity gradient in a direction transverse with respect to the strap, i.e., in a longitudinal direction of the boot.
Such a construction therefore makes it possible to limit the “string” effect, i.e., the overpressure effect produced by a tightening element that is more or less wire-shaped by distributing the tightening forces through the transverse tongues.
Such an insert shape allows undeniable improvements with respect to the existing tightening straps; however, the insert shapes are limited given the requirements of assembly by stitching to the other layers of the strap.